The core of OS X is BSD, a Unix variant that has the reputation for being bulletproof. BSD isn't as popular in the market as Linux because it has a reputation for being harder to install and administer. However, it's so rock-solid that many commerical websites use it.

Adding a solid GUI on top of a Unix-like core is nothing new. NeXT (Steven Job's old company) ran on Mach, a microkernel architecure that was pretty Unix-like. OS X is also built on the Mach kernel.

While I've never used OS X, I've heard plenty of good things about it. I like competition - it keeps companies from being complacent. Your other point is well taken - if people can buy OS X for the Intel, they wouldn't need to buy the somewhat pricey (but good) Mac hardware. That'll likely be one of the most important decision points for whether OS X Intel is ever released. Software support for the new architecture is also critical. Stay tuned, this could get real interesting.